Monomethylammonium ion has been shown to be a monovalent cation activator for muscle pyruvate kinase and has been found to be a useful probe for physical studies of the interaction of monovalent cations with this enzyme. A thorough frequency dependence of the effect of the enzyme bound Mn2 ion on the spin lattice relaxation time (1/T1) of the carbon-bound protons of methylammonium ion by high resolution pulsed nmr is being done to determine a precise correlation time (Tc) for the electron-nuclear interaction and thus obtain a more precise measurement of the interatomic distances of the two cations. Since the monovalent cation-divalent cation distance in the enzyme complex is dependent on the conformation of the enzyme as determined by the substrates bound, a complete study of the effects of the various ligands on the conformational state of the enzyme will be undertaken to attempt to describe the structure of the substrates and the role of the cations in pyruvate kinase catalysis. The enzyme phosphoenolpyruvate carboxykinase from chicken liver has been purified to near homogeneity as determined by specific activity. A homogeneous preparation is to be prepared and the metal ion requirements for activity will be studied kinetically. The structure of water bound to the enzyme-Mn2 ion complex will be determined by nmr techniques as will the structure of the substrates about the bound cation.